L1CTL: Add support for CCCH_MODE_COMBINED_CBCH

In OsmocomBB/trxcon Change-Id Ia94ebf22a2ec439dfe1f31d703b832ae57b48ef2
we introduced a new mode CCCH_MODE_COMBINED_CBCH to indicate that the
channel combination is a CCCH+SDCCH/4 with one SDCCH stolen for CBCH.

Let's make sure we actually use that mode in our CBCH related tests

Change-Id: I27ee2c81bec7175c1ea09d4f3f6037f2866fe242
diff --git a/bts/BTS_Tests_SMSCB.ttcn b/bts/BTS_Tests_SMSCB.ttcn
index 0712a90..c02522b 100644
--- a/bts/BTS_Tests_SMSCB.ttcn
+++ b/bts/BTS_Tests_SMSCB.ttcn
@@ -216,7 +216,7 @@
 	f_init(testcasename());
 
 	f_init_l1ctl();
-	f_l1_tune(L1CTL);
+	f_l1_tune(L1CTL, ccch_mode := CCCH_MODE_COMBINED_CBCH);
 	/* FIXME: switch to dedicated mode for SDCCH/8 */
 
 	/* send SMSCB[s] via RSL */